Threedimensional - Architected Materials And Structures .

2y ago
16 Views
2 Downloads
3.72 MB
8 Pages
Last View : 14d ago
Last Download : 2m ago
Upload by : Oscar Steel
Transcription

Three-dimensional architected materialsand structures: Design, fabrication, andmechanical behaviorJulia R. Greer and Vikram S. Deshpande, Guest EditorsThe integration of materials and architectural features at multiple length scales into structuralmechanics has shifted the paradigm of structural design toward optimally engineeredstructures, which resulted in, for example, the Eiffel Tower. This structural revolution pavedthe way for the development of computational design approaches used in modern-dayconstruction. Similar principles are now being applied to the design and manufacture ofarchitected materials with a suite of properties determined a priori and attained throughmultiscale approaches. These new material classes potentially offer breakthrough advancesin almost every branch of technology: from ultra-lightweight and damage-tolerant structuralmaterials to safe and efficient energy storage, biomedical devices, biochemical, andmicromechanical sensors and actuators, nanophotonic devices, and textiles. When reducedto the microscale, such materials embody the characteristics of both the constituentmaterial, which brings the effects of its microstructure and ensuing properties at the relevantcharacteristic length scales, as well as the structure, which is driven by architected design.This issue gives an overview of the current state of the art of this new class of materials.IntroductionThe development of new engineering materials closely mirrored the ages of human development, with the particularperiods of history labeled by the materials used in those eras.For example, the tools and weapons of prehistory, 300,000 ormore years ago, were bone and stone; that period is referredto as the Stone Age. The discovery of ways to reduce ferrousoxides to make iron, a material with greater stiffness, strength,and hardness than any other then available, occurred around1450 BC. However, two millennia passed before the blastfurnace was developed in 1500 AD, enabling the widespreaduse of cast iron in the Iron Age. The development of newmaterials significantly accelerated the industrial revolution,and with the addition of polymers to the suite of materialsavailable to engineers, enabled developments in multipletechnologies.One way to examine the availability of engineering materialsto possess a given set of properties is via material property chartsor so-called “Ashby charts.”1 Material property charts display materials on axes based typically on two of their properties. Materials have many properties of course—mechanical,thermal, electrical, optical, and many more—so the numberof such pair-wise combinations is large. Each chart can thusbe thought of as a slice through “material property space”—amultidimensional space with material properties as its axes.Figure 1 shows one such multidimensional chart displaying the relation between strength, modulus, and density ofengineering materials. There are many obvious incentives forseeking materials with greater strength: more durable andeffective tools; faster, more economical transport; and larger,more daring structures. In recent times, it has been highstrength at low weight that is frequently sought, with transportand aerospace as the direct drivers.All such material property charts contain regions that aredensely populated with materials, and other parts that are notpopulated—in the so-called “white spaces.” Some regionsare inaccessible for fundamental reasons related to the sizeof atoms and the nature of the forces that bind them together.Other parts are empty even though, in principle, they couldbe filled. One approach to filling holes in material propertyspace is by manipulating chemistry, developing new metalalloys, new polymer formulations, and new compositionsof glass and ceramic that extend the populated areas of theproperty charts. A second is by manipulating microstructure,Julia R. Greer, California Institute of Technology, USA; jrgreer@caltech.eduVikram S. Deshpande, Department of Engineering, University of Cambridge, UK; vsd20@cam.ac.ukdoi:10.1557/mrs.2019.232750 VOLUME 44 OCTOBER 2019 www.mrs.org/bulletin 2019MaterialsDownloaded MRSfromBULLETINhttps://www.cambridge.org/core.IP address:209.126.7.155, on 22 Apr 2021 at 19:58:45, subject to the Cambridge Core terms of s. https://doi.org/10.1557/mrs.2019.232Research Society

THREE-DIMENSIONAL ARCHITECTED MATERIALS AND STRUCTURES: DESIGN, FABRICATION, AND MECHANICAL BEHAVIORFigure 1. An Ashby plot of engineering materials showing the relation of strength, modulus, and density. The white spaces on these plotsrepresent opportunities for the development of new materials, although some of these white spaces are inaccessible for fundamental reasonsrelated to the size of atoms and the nature of the forces that bind them together.1using thermomechanical or thermochemical processing to control the distribution of phases and defects within materials. Bothhave been exploited systematically for many decades, leavinglittle room for further gains. A third approach is that of controlling architecture to create hybrid materials—combinations ofmaterials or of materials and space in configurations that offerenhanced performance. A relatively well-known exampleof such an architecture is carbon fiber-reinforced composites,which have been highly successful in replacing structural metals for lightweight applications (e.g., the Airbus A350-XWBaircraft airframe has 50% carbon fiber composite by weight).A key feature of hybridization and architecting is that synergistic effects can be exploited to achieve more than the“sum of the parts” (glass fiber-reinforced epoxy is muchtougher than either constituent due to the synergistic effectof distributed cracking). VOLUMEBULLETIN44 OCTOBER2019 www.mrs.org/bulletinDownloaded from https://www.cambridge.org/core. IP address: 209.126.7.155, on 22 Apr 2021 at 19:58:45, subjectMRSto theCambridgeCore termsof use, availableathttps://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs.2019.232751

THREE-DIMENSIONAL ARCHITECTED MATERIALS AND STRUCTURES: DESIGN, FABRICATION, AND MECHANICAL BEHAVIORRecent major technological advances have opened pathways to create architected “metamaterials” that have thepotential to solve key challenges in our society. These includedevelopment of (1) nano- and microscale fabrication processes with precise control of material chemical composition,morphology, and topology; (2) mathematical tools for theconstruction of material property bounds; (3) computationalcapabilities that permit accurate simulation and prediction ofeffective materials properties as a function of constituent phases, and the arrangement of microstructural features at variouslength scales; and (4) experimental characterization methodswith resolutions capable of quantifying and measuring thechemical and morphological constructs of architected features.For example, we can envisage devices and materials generated by nanoscale additive manufacturing that can fundamentally change conventional technologies in the realms ofelectronics, optoelectronics, energy storage and harvesting,biochemical sensors, and many others. One could also imagine that these devices—powered, actuated, and controlledremotely—could be freely dispersed in foreign environments forubiquitous sensing, injected into the blood stream for whole bodyimaging, or integrated with molecules for designed drug delivery.Architected materialsThe term “architected material” first used in an overview paperby Ashby and Bréchet2 was coined to make a link betweenthe practice in architecture and structural engineering of topology optimization that has been employed to produce reliable,light, and elegant constructions. An architected material is acombination of several simple materials, possibly involvingopen space, configured to reach performances not offered byany individual material. Hence, there is a clear target in termsof a set of properties and performance to optimize at the onset,which motivates and guides its development. To focus thescope of this issue of MRS Bulletin, we limit attention to theextreme case of porous solids (a hybrid of solid and air), andexplore the effects of micro-architecture, length scale, and constituent solid material on properties. Some representative examples of nano- and micro-architected materials that are createdusing various additive manufacturing and three-dimensional(3D) printing techniques are shown in Figure 2.3–6Topological designFleck et al.7 defined a general lattice material as a cellular, reticulated, truss, or lattice structure made up of a large number of uniform lattice elements (e.g., slender beams or rods) and generatedby tesselating a unit cell, comprised of just a few lattice elements,throughout two- (2D) or three-dimensional (3D) space. This shallserve as our working definition of an architected material.Classically, periodic planar (i.e., 2D) lattices are classifiedas regular, semi-regular, or other. Regular lattices are generated by tessellating a regular polygon to fill the entire plane.8Only a few regular polygons produce such a lattice—theseare the triangle, square, and hexagon. Semi-regular latticesare generated by tessellating two or more different kinds of752regular polygons to fill the entire plane; only eight independentsemi-regular lattices exist, for example, the triangular-hexagonallattice, also known as the kagome lattice.9,10 Additional planefilling lattices can be constructed from two or more polygonsof different sizes, or by relaxing the restriction that each jointhave the same connectivity. Spatial or 3D lattices can be generated by filling space with polyhedra. Of the regular polyhedrawith a small number of faces only the cube and the rhombicdodecahedra can be tessellated to fill all space.11 Typically,spatial lattices are constructed using combinations of differentpolygonal structures. For example, tetrahedra and octahedramay be packed to form the octet-truss lattice.12The relative density ρ of a lattice material is defined asthe ratio of the unit cell solid fill fraction in the unit cell tothe density of the solid. Lattice materials resemble frameworks when ρ is less than about 0.2, and in this regimeρ is directly related to the thickness t and length l of a slender strut according to ρ (t /ℓ) and ρ (t /ℓ ) 2 in two dimensions and three dimensions, respectively. In the classicallimit of slender-beam architectures, there are two distinctspecies of cellular solids. The first, typified by foams, arebending-dominated structures; the second, typified by triangulated micro-architected solids structures, are stretchingdominated—a distinction most evident in their mechanicalproperties.13 To give an idea of the difference, a foam witha relative density of 0.1 (meaning that the solid cell wallsoccupy 10% of the volume) is a factor of three less stiffthan a triangulated lattice of the same relative density. Thedistinction between a bending-dominated and a stretchingdominated structure is largely dictated by the connectivityof joints rather than by the regularity of the microstructure,and is closely linked to the collapse response of a pin-jointedstructure of the same morphology. If the parent, pin-jointedlattice exhibits collapse mechanisms that generate macroscopic strain, then the welded-joint version relies upon therotational stiffness and strength of the nodes and struts forits macroscopic behavior. Consequently, the parent latticeis bending-dominated. In contrast, when the parent lattice haseither only periodic or no collapse mechanisms, the weldedjoint version is stretching-governed. The necessary, but notsufficient, condition for rigidity is Z 4 in two dimensionsand Z 6 in three dimensions, where Z is nodal connectivity.13Fleck et al.7 used this idea to construct a Venn diagram toillustrate the various types of mechanisms exhibited by classesof 2D periodic pin-jointed trusses, as shown in Figure 3.Consider a fully triangulated structure, comprising equilateral triangles with a nodal connectivity of Z 6; it is highlyredundant and possesses no collapse mechanisms. In contrast,a triangular-triangular lattice collapses by a mechanism thatleads to a macroscopic hydrostatic strain. Thus, this structurehas zero macroscopic stiffness against this collapse mode. Thekagome microstructure has a connectivity of Z 4 and has nostrain-producing collapse mechanisms; it can only collapseby periodic mechanisms, which do not produce a macroscopicstrain. Consequently, it is rigid in all directions. The cases VOLUME 44 OCTOBER 2019 www.mrs.org/bulletinDownloaded MRSfromBULLETINhttps://www.cambridge.org/core.IP address:209.126.7.155, on 22 Apr 2021 at 19:58:45, subject to the Cambridge Core terms of use, available athttps://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs.2019.232

THREE-DIMENSIONAL ARCHITECTED MATERIALS AND STRUCTURES: DESIGN, FABRICATION, AND MECHANICAL BEHAVIORFigure 2. (a) A scanning electron microscope (SEM) image of the second-order octahedron of an octahedral lattice showing the first-orderrepeating units that make up the structure.3 Scale bar 10 μm. (b) Truss architecture and geometry definitions: (i) unmodified circularstrut of radius, r, and length, l; (ii) square-modified strut; (iii) star-modified strut; (iv) uniaxial compression of a 3 3 3 reduced-orderoctahedron model; (v) octahedron node substructures depicting the tetrahedral mesh and the retained degrees of freedom (DOF) pointsin red; (vi) uniaxial compression of a 3 3 3 reduced-order tetrakaidecahedron model; and (vii) tetrakaidecahedron node substructuresdepicting the tetrahedral mesh and the retained DOF points in red. (c) SEM image of a “woven” octahedron nanolattice where each beam iscomposed of three woven beams woven into a spiral. Scale bar 20 μm. Image and sample produced by W. Moestopo and C.M. Portela,California Institute of Technology. (d) SEM image of a bi-phase hollow alumina nanolattice with 10-nm-thick walls that shows two distinctrelative densities, of 0.87% in the top half and 0.43% in the bottom half. Scale bar 50 μm. Image and sample produced by M. Lifson,California Institute of Technology. (e) Uniaxial compression data for the nanolattice shown in (d).4 (f) Additive manufacturing of polymerderived ceramics using polymer waveguide technique followed by pyrolysis. Reprinted with permission from Reference 6. 2016 AAAS.(g) Solid-beam glassy carbon lattice made by direct laser writing and subsequent pyrolysis. Scale bar 1 μm. Reprinted with permissionfrom Reference 5. 2016 Nature Publishing Group.of the square lattice and hexagonal lattice, with Z 4 andZ 3, respectively, are different. Each of these structures cancollapse by macroscopic strain-producing mechanisms and byperiodic collapse mechanisms. The main conclusion to drawfrom Figure 3 is that the fully triangulated structure is macroscopically stiff because it possesses no collapse mechanisms,while the kagome structure is macroscopically stiff becauseit has only periodic collapse mechanisms, which generate nomacroscopic strain.Since nodal connectivity controls whether the deformation of a lattice is stretch or bend-dominated, this is directlyreflected in the scaling expressions of their strength andstiffness with relative density. Simple beam theory dictatesthat the Young’s modulus and strength of lattice materials,made from a solid material of Young’s modulus ES (where thesubscript S stands for solid), and yield strength σYS (wherethe subscript YS stands for yield strength), are related to theirrelative density via scaling laws of the form:E Aρ n , Es(1a)σY Bρ m , σYS(1b)andrespectively. The coefficients (A, B, n, m) for some common2D lattices are listed in Table I.First, consider the case of stiffness. The hexagonal latticeis bending-dominated, with n 3. In contrast, the kagomeand fully triangulated lattices are stretching-dominated withn 1. Remarkably, the coefficient A is identical for the triangulated and kagome lattices. These lattices have identical effective properties, and each achieves the Hashin–Shtrikman14upper bound—the tightest possible bound for a bi-materialcomposite with two different moduli. The differences betweenthe two lattices, however, show up when imperfections VOLUMEBULLETIN44 OCTOBER2019 www.mrs.org/bulletinDownloaded from https://www.cambridge.org/core. IP address: 209.126.7.155, on 22 Apr 2021 at 19:58:45, subjectMRSto theCambridgeCore termsof use, availableathttps://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs.2019.232753

THREE-DIMENSIONAL ARCHITECTED MATERIALS AND STRUCTURES: DESIGN, FABRICATION, AND MECHANICAL BEHAVIORLength scale and effects of nanoarchitectingIn the last 15 years, it was ubiquitously demonstrated that at the micron- and submicronscales, the sample size dramatically affectscrystalline strength, as revealed by roomtemperature uniaxial compression and tensionexperiments on a wide range of single-crystallinemetallic nanopillars.19,20 To date, these microand nanodeformation studies (both compression and tension) include (but are not limitedto) fcc metals (Ni and Ni-based superalloys),Au, Cu, Al (as-fabricated and intentionallypassivated), bcc metals (Mo, Ta, W, V, Nb),hexagonal close-packed metals (Ti and Mg),tetragonal low-temperature metals, GumFigure 3. Venn diagram for the classification of the deformation mechanisms of selectedmetal, nanocrystalline metals (Ni, Pt, and72D lattices.Cu), shape-memory alloys, and a variety ofmetallic glasses.19 Most of these experiments,where the initial microstructure contained dislocations orare introduced. For example, by randomly perturbing theother defects, revealed a remarkable dependence of thelocation of the nodes at fixed relative density, there is a largeattained flow strength on sample diameter due to the presdrop in the modulus of the kagome lattice, but a much smallerence of unique defect-driven deformation mechanisms indrop in modulus of the triangulated lattice.15 This is becausenanoscale plasticity, often characterized by discrete strainthe triangulated lattice has a higher nodal connectivity of Z 6bursts and size-dependent stress–strain relationships. Thesethan the kagome lattice (Z 4) and is a much more redundantfindings suggest that when the extrinsic sample size isstructure when the struts are assumed to be pin-jointed at thereduced to that on the order of or below the characteristicnodes.microstructural length scale of the material, size reductionThe main conclusions for stiffness carry over to strengthhas a significant effect on material strength and susceptiwith m 1 for the triangular and kagome structures thatbility to failure through the activation of unique deformadeform by bar stretching, while the hexagonal honeycombtion mechanisms, pertinent to surface-dominated nano- anddeforms by bar bending, leading to m 2. Similarly, scalingmicron-sized materials. Nearly all classes of materials—laws have been developed for a host of 3D lattice materials,ceramics, glasses, metals, and semiconductors—exhibit sizewith the primary conclusions carrying over from the 2D case.effects when their dimensions are reduced to the nanometerFor example, the octet truss, identical in crystal structure toand submicron scales. These size effects manifest themselvesface-centered cubic (fcc), has a nodal connectivity (coordinain a range of mechanical properties; for example, smallertion number) of 12 and is a stretching-dominated structure.can be stronger (single crystalline metals) or weaker (nanoThe Young’s modulus E and yield strength σYS scale linearly withcrystalline metals). Reducing structures to nano- or micronrelative density such that E 0.3ρES and σYS 0.3ρσYS . Theselevels can suppress failure in intrinsically brittle materialsvalues are close but not equal to the Hashin–Shtrikman upper(glasses and ceramics) and c

property charts. A second is by manipulating microstructure, Threedimensional - architected materials and structures: Design, fabrication, and mechanical behavior Julia R. Greerand Vikram S. Deshpande Guest Editors The integration of materials and ar chitectural features at multiple length scales into structural

Related Documents:

Well-Architected Framework Introduction The AWS Well-Architected Framework helps you understand the pros and cons of decisions you make while building systems on AWS. By using the Framework, you will learn architectural best practices for designing and operating reliable, secure, effic

Inflight Advertising Initiative "Embedded" IFE is architected to reduce weight and heat in the inflight environment. Architected around a 2-year development, 10-year deployment cycle. Supported by a 30-day exhibition cycle and a 45-60 day advance delivery schedule. PEDs emerging as the client-side of the IFE network.

AWS Well-Architected Frameworkとは? AWS Well-Arch

structures and materials. 3 . structures and materials . Background . MUSEUM IN A BOX. Materials . of a composite material was a mix of mud and straw that was used to make bricks. Composites have two . intended to build a passenger aircraft predominately out of composite materials. This aircraft, the Boeing 787 (Img. 3), took light for the .

Chapter 9 Hydraulic Structures September 2017 Urban Drainage and Flood Control District 9-1 Urban Storm Drainage Criteria Manual Volume 2 . Structures in Streams . Hydraulic structures are used to guide and control water flow in streams. Structures described in this chapter consist of grade control structures and

Manufactured Structures Many things built by people are manufactured structures.The largest buildings, the tiniest beads, a complicated jigsaw puzzle, and a simple spoon are all manufactured structures.Many manufactured structures are modelled after natural structures. A fishing net, f

difference between homologous and analogous structures is that homologous structures are derived from a common ancestral structure while analogous structures are derived from different evolutionary ancestries. What are Homologous Structures? Homologous structures ar

“Am I My Brother’s Keeper?” Cain & Abel by Tintoretto. Everything can be taken from a man but the last of the human freedoms - to choose one’s attitude in an given set of circumstances, to choose one’s own way.--Auschwitz Survivor, Victor E. Frankl Human Gene Map. OnegShabbat Archives –Emanuel Ringleblum Remembrance: To record and to teach future Generations. The time has come to .